1. Field of the Invention
The present invention relates to a resin-sealed electronic control device suitable, for example, as an on-vehicle electronic control device, and a method of fabricating the same.
2. Description of the Related Art
As a control device for an automobile transmission, an integrated resin-sealed electronic control device mounted inside the transmission is widely put into practical use. The on-vehicle electronic control device as described above includes any one of a ceramic board and a polyimide board bonded to a support plate serving as a thermal diffuser plate. The entire on-vehicle electronic control device except for a part of external connection terminals and a part of the support plate is integrally formed with a thermosetting resin.
For example, the invention entitled “Electronic Circuit Apparatus and Method of Manufacturing the Same”, which is described in Japanese Patent Application Laid-open No. 2004-281722 (FIG. 1 and Abstract), discloses a resin-sealed electronic circuit apparatus with a high heat-dissipating property and a high packaging density in applications where high hermetic-sealing property and durability are required. In the electronic circuit apparatus, at least two wiring boards, on which electronic components are mounted, are fixedly bonded to a highly thermally conductive thermal diffuser plate through an intermediation of an adhesive. The entire wiring boards, the entire thermal diffuser plate, and a part of an external connection terminal are hermetically sealed by and integrally molded with a thermosetting resin composition. In this manner, the small and highly reliable electronic circuit apparatus can be provided at low cost.
Specifically, the aforementioned electronic circuit apparatus includes: a multilayered wiring board on which at least two electronic components are mounted; a polyimide wiring board on which heating elements are mounted; the thermal diffuser plate having a higher thermal conductivity than those of the multilayered wiring board and the polyimide wiring board; and an external connection terminal. The electronic circuit apparatus is a control unit for an automobile, which has the following structure. The multilayered wiring board is fixedly bonded to one surface of the thermal diffuser plate through an intermediation of the adhesive, whereas the polyimide wiring board is fixedly bonded to the other surface of the thermal diffuser plate through an intermediation of an adhesive. The polyimide wiring board is bent to be fixedly bonded so that an upper surface and a lower surface of the thermal diffuser plate are connected to each other. In this manner, the polyimide wiring board and the multilayered wiring board are electrically connected to each other. The multilayered wiring board, the polyimide wiring board, and the external connection terminal are electrically connected to each other. The entire surface of the multilayered wiring board, the entire surface of the polyimide wiring board, a part of the thermal diffuser plate, and a part of the external connection terminal are integrally molded with the thermosetting resin composition. The multilayered wiring board and the polyimide wiring board, and the external connection terminal are connected to each other by a bonding wire.
In the invention entitled “Electronic Circuit Apparatus and Method of Manufacturing the Same” described in Japanese Patent Application Laid-open No. 2004-281722 cited above, the wiring board is divided into two pieces so as to be fixedly bonded onto two surfaces of the thermal diffuser plate. As a result, an area of the wiring board is halved, while the heat-dissipating property is improved. The polyimide wiring board (flexible board) is used as one of the wiring boards so that the polyimide wiring board is bent to be connected to the ceramic board which is the other board.
However, each of the wiring boards is a one-sided board for bonding to the thermal diffuser plate. Therefore, in order to ensure an area on which the circuit components are mounted, the area of each of the wiring boards is disadvantageously increased.
Moreover, if the area of each of the wiring boards is large, there is another problem in that the wiring board is likely to be separated from a molded exterior covering material with repeating changes in temperature due to a difference in linear expansion coefficient.